Pyrotechnic charge

ABSTRACT

A pyrotechnic charge for production of IR radiation, which is characterized in that a brominated compound is included as a fuel and/or as an oxidant and/or as a binder. A pyrotechnic charge such as this can be used, for example, to produce an IR decoy with β-band spectral matching.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pyrotechnic charge for production ofinfrared (IR) radiation, and in particular to a pyrotechnic charge suchas this for use in spectrally matched IR decoys.

In the military field, missiles such as air-to-air and surface-to-airguided missiles are used to attack airborne targets, such as jetaircraft, helicopters and transport aircraft, which find the directionof and track the infrared (IR) radiation which originates from thetarget engine, primarily in the band between 0.8 and 5 μm, by means of asearch head which is sensitive to IR radiation. Decoys (also referred toas flares) are therefore used as defence against these missiles, andimitate the IR signature of the target in order to deflect approachingguided missiles. Decoys such as these can also be used preventively, inorder to exacerbate or even to prevent the detection of targets, byreducing the contrast in the scene.

One typical effective substance for production of black-body radiationin the IR band is a pyrotechnic charge composed of magnesium,polytetrafluoroethylene (Teflon®) and vinylidenefluoridehexafluoroisoprene copolymer (Viton®), also referred to as MTV, whosespectral intensity distribution is similar to that of a black bodyduring combustion. The actual signature of, for example, aircraftengines differs from the signature of a black-body radiator, however,since the hot exhaust gases from propeller or jet propulsion systemsemit strong selective components in the wavelength band between 3 and 5μm (so-called β band). This selective radiated emission is caused by thecombustion products CO and CO₂, which emit at 4.61 μm and 4.17 mm,respectively.

In order to distinguish between decoys with a black-body signature andreal airborne targets, modern search heads therefore additionally carryout a spectral assessment of the radiation source. In particular, thistakes account of the fact that the integrated intensity of the signatureof an aircraft or of its engine is greater by a factor of 2 in thewavelength band between 3 and 5 μm (β band) than the integratedintensity in the wavelength band between 2 and 3 μm (so-called α band).In contrast, this ratio is always less than 1 for decoys with ablack-body signature.

2. Discussion of the Prior Art

In order to overcome the capability of search heads to spectrallydistinguish decoys on this basis, matched decoys have been proposed inthe past, which have a spectral intensity distribution similar to anaircraft. Conventional pyrotechnic effect charges such as these forspectrally matched IR decoys typically contain carbon-rich compoundstogether with powerful oxidants, such as perchlorates. Typicalformulations for apparent targets such as these are composed ofpotassium perchlorate (KClO₄), potassium nitrate (KNO₃) and mellitictrianhydride (C₆(C₂O₃)₃)—see for example U.S. Pat. No. 6,427,599 B1,composed of potassium perchlorate and potassium benzoate (KC₇H₅O₂)—seefor example US 2004/0011235 A1, or composed of potassium perchlorate andhexacyanobenzene (C₆(CN)₆)—as described, for example, in subsequentlypublished DE 10 2004 024 857 A1 by the same applicant.

Table 1, below, shows typical compositions of the spectrally matchedeffective substances disclosed in the patent documents cited above:

TABLE 1 US US 6,427,599 B1 2004/0011235 A1 DE 10 2004 024 857 KClO₄ 6065 65 KC₇H₅O₂ 35 C₆(C₂O₃)₃ 35 KNO₃ 5 C₆(CN)₆ 35

The above numerical details are in each case in the form of proportionsby mass as % by weight, in which case a binder is in each case added tothe substances formed in this way, in a proportion by weight of 5:100.

Furthermore, the applicant recently proposed the use of deuterizedcompounds as oxidants and/or as fuels for spectrally matched apparenttargets—as in the above-referenced published DE 10 2004 024 857 A1.

SUMMARY OF THE INVENTION

The present invention is based on the object of providing a pyrotechniccharge for production of IR radiation, which produces a spectralintensity distribution similar to that of an aircraft during combustionof the fuels. One particular aim is for the integrated radiationintensity in the long-wave β band during combustion of the fuels in thepyrotechnic charge to be better matched to that of the signature of anaircraft.

The inventive pyrotechnic charge for production of IR radiationaccording to a first aspect of the invention is characterized in that abrominated compound is included as a fuel and/or as an oxidant.According to a second aspect of the invention, a brominated compound isincluded as a fuel and/or as an oxidant and/or as a binder.

The use of brominated compounds, or compounds containing bromine, as afuel, oxidant and/or binder leads to increased selective radiatedemission in the □ band and at the same time to reduced selectiveradiated emission in the α band, so that the quotient of the integratedradiation intensities in the □ band and the α band during combustion ofthe fuels in the pyrotechnic charge according to the invention is bettermatched to that of the signature of an aircraft.

In one refinement of the invention, the molar ratio of Br/H in thebrominated compound or compounds is ≧0.5; and the molar ratio ofBr/M^(n+) in the brominated compound or compounds is ≧n, where M is analkali or alkaline-earth metal.

By way of example, one or more compounds from the group comprisingbrominated hydrocarbons with a melting point of >100° C., brominatedaromatic compounds, brominated aromatic carbonyl compounds, brominatedaromatic carboxylic acids and lactones may be included as a fuel.

One or more compounds from the group of alkali and alkaline-earth metalbromates and perbromates, and/or one or more compounds from the group ofalkali and alkaline-earth metal nitrates, dinitramides and peroxides maybe included as oxidants.

In one preferred embodiment of the invention, the fuel is included in aproportion by mass of approximately 10% to approximately 55%, theoxidant in a proportion by mass of approximately 40% to approximately85%, and the binder in a proportion by mass of 0% to approximately 5%.

DETAILED DESCRIPTION OF THE INVENTION

The invention as explained above is in this case based on theconsiderations described in the following text.

According to the invention, the aim is to provide a pyrotechnic chargewhich concentrates to a greater extent selective radiated emissioncomponents in the desired long-wave β band, that is to say thewavelength band from approximately 3.5 to 4.8 μm, during combustion ofthe fuels, in order to better imitate the signature of an aircraftengine.

The previous development by the same applicant, as cited above, to usedeuterized compounds as oxidants and/or as fuels for spectrally matchedapparent targets is based on the idea of bathochromic shifting of themolecular bands of H₂O and HCl created during the combustion ofsubstances containing hydrogen. While H₂O and HCl have resonantwavelengths of 2.73 μm and 3.43 μm, respectively, and are thereforedisadvantageous in terms of the spectral ratio, and/or are outside thesuitable long-wave spectral band, the resonant frequencies of thedeuterated compounds HDO, D₂O and DCl appear at 3.67 μm, 3.74 μm and4.66 μm, respectively, and therefore in each case within theadvantageous long-wave β band between approximately 3.5 and 4.8 μm.

Until now, there have been no reports on other options for spectralmatching by bathochromic or hypsochromic (long-wave or short-wave)shifting in the past. No other option has been previously known eitherfor influencing the H₂O/CO₂ ratio advantageously than by the choice offuels with a suitable C/H ratio.

The present invention solves the problem of spectral matching andmatching of the C/H ratio by the use of compounds containing bromine.

The advantageous characteristics of pyrotechnic compositions containingbromine are in this case a result of the following circumstances:

-   -   the replacement of hydrogen in organic fuels by bromine leads to        an increase in the C/H ratio and thus to suppression of the H₂O        emission in the short-wave spectral range of the α band between        2 and 3 μm;    -   the bromine that is introduced produces hydrogen bromide (HBr)        during combustion, whose band centre is located at 3.91 μm, in        the long-wave spectral range within the β band;    -   together with oxidants such as nitrates and peroxides based on        alkali and alkaline-earth metals, bromine introduced via the        fuel results in volatile bromides and thus reduces the tendency        for condensation in the flame zone, which in turn reduces the        proportion of disturbing continuum radiation in the flame, which        would have a disadvantageous influence on the band ratio;    -   in the case of replacement of perchlorates by chlorine-free or        brominated oxidants, the radiated emission of the HCl band at        3.34 μm can be prevented or shifted.

Suitable bromine compounds for modification of the C/H ratio for thepurposes of the invention are brominated organic compounds, such asperbrominated aromatic compounds which, in addition to bromine, can alsocarry oxygen in the form of carbonyl and ether groups.

Suitable compounds including their [CAS No.] for the purposes of theinvention are listed in the following text, without any intention of thepresent invention being restricted only to these specific compounds:perbromo (diphenyl ether) ((C₆Br₅)₂O) [1163-19-5], available, forexample, under the trade mark Saytex 102; hexabromobenzene (C₆Br₆)[87-82-1]; tetrabromo-p-benzoquinone (C₆Br₄(═O)₂) [488-48-2];tetrabromo-o-benzoquinone (C₆Br₄(═O)₂) [2435-54-3]; tetrabromophthalicanhydride (C₆Br₄C₂O₃) [632-79-1]; tetrabromophenolphthalein(C₂₀H₁₀Br₄O₄) [1301-20-8]; tetrabromohydroquinone (C₆Br₄(OH)₂)[2641-89-6]; tetrabromocyclohexadienone (C₆H₂Br₄O) [20244-61-5];tetrabromocatechol (C₆Br₄(OH)₂) [488-47-1]; dibromobiphenyl (C₆H₄Br)[92-86-4]; dibromofluoresceine (C₂₀H₁₀Br₂O₅) [596-03-2];dibromonaphthoquinone (C₁₀H₄Br₂O₂) [13243-65-7];dibromohydroxynaphthalene (C₁₀H₆Br₂O) [16239-18-2];dibromo-4-nitroaniline (C₆H₂(NO₂)NH₂Br₂) [827-94-1]; dibromonitrophenol(C₆H₂NO₂Br₂OH) [99-28-5]; and dibromonitrobenzene (C₆H₃NO₂Br₂)[3460-18-2].

When using bromocarbon compounds as fuels, additional fuels containinghydrogen can also be used up to a molar ratio Br/H of 1/1 depending onthe proportion of bromine and the Br/H ratio, so that all of thehydrogen can be converted to HBr. For example, when usingdecabromo(diphenyl ether) as a carbon source, an equimolar amount ofanthracene can be used as a carbon source, if all of the protons areintended to be converted into HBr as shown by the following example ofthe reaction of 1 mol of decabromo(diphenyl ether) with 1 mol ofanthracene:

1 (C₆Br₅)₂O+1C₁₄H₁₀43 26 {C}+10HBr+1O

The temperature-dependent, integrated band intensity α_(j) for the HBrmolecule was determined recently by S. P. Fuβ, A. Hamins in“Determination of Planck Mean Absorption Coefficient for HBr, HCl andHF” in Journal of Heat Transfer, 124, 2002, pages 26-29. Table 2, below,shows the comparison of the band intensity at 300 K for the moleculesCO₂, CO, HCl and HBr.

TABLE 2 Band Spectral range of centre [cm⁻¹, Integrated band intensityMolecule the band [cm⁻¹] μm] at 296 K [atm⁻¹cm⁻²] CO₂ 2325-2410 2325,4.30 2700 CO 1795-2317 2143, 4.67 250 HCl 2399-3161 2885, 3.47 155 HBr2123-2791 2559, 3.91 35

The low band intensity of HBr in comparison to HCl and CO₂ indicatesthat HBr is not in fact a suitable spectral emitter, but can be used formodification of conventional effect charges owing to the position of itsband centre and the low intensity.

Conventional spectrally matched effect charges based on perchlorates andperoxides produce condensed reaction products during combustion, such ascarbonates (K₂CO₃) and oxides (BaO), which increase the continuumradiation and thus cause the spectral ratio to deteriorate. In thepresence of bromine or hydrogen bromide from the flame, the formation ofcondensed products can be prevented in-situ since appropriate bromidesare created. Within the flame, these are gaseous up to temperatures ofapproximately 1200° C. or 1000° C., and do not condense until outsidethe flame zone.

According to the invention, the proportion of bromine is thus preferablyset such that any alkali or alkaline-earth metal ions, such as K⁺ orBa²⁺, can be converted by means of Br₂ or HBr to KBr or BaBr₂,respectively.

The bromates and perbromates of the following general compositions arepreferably used as oxidants

MBrO₃ where M=NH₄, Li, Na, K, Rb, Cs,M(BrO₃)₂ where M=Mg, Ca, Sr, Ba,MBrO₄ where M=NH₄, Li, Na, K, Rb, Cs, andM(BrO₄)₂ where M=Mg, Ca, Sr, Ba.

Further suitable oxidants for the purposes of the invention are thenitrates and dinitramides of the alkali and alkaline-earth metals withthe following general compositions:

MNO₃ where M=NH₄, Li, Na, K, Rb, Cs,M(NO₃)₂ where M=Mg, Ca, Sr, Ba,MN₂O₄ where M=NH₄, Li, Na, K, Rb, Cs, andM(N₂O₄)₂ where M=Mg, Ca, Sr, Ba,as well as the peroxides of lithium and of the alkaline-earth metalsM₂O₂ where M=Li, Na, andMO₂ where M=Mg, Ca, Sr, Ba.

In all of the fuels and oxidants mentioned above, the proportion by massof the fuel in a pyrotechnic charge for production of IR radiationaccording to the invention is preferably approximately 10% toapproximately 55%, the proportion by mass of the oxidant isapproximately 40% to approximately 85%, and the proportion by mass ofthe binder is from 0% to approximately 5%.

The pyrotechnic charges with the compounds stated above canadvantageously be used for IR decoys since the integrated radiationintensity in the long-wave β band during combustion of the fuels in thepyrotechnic charge is better matched to that of the signature of anaircraft.

1. Pyrotechnic charge for production of IR radiation, wherein abrominated compound is included as a fuel and/or as an oxidant. 2.Pyrotechnic charge for production of IR radiation, wherein a brominatedcompound is included as a fuel and/or as an oxidant and/or as a binder.3. Pyrotechnic charge according to claim 1 or 2, wherein the molar ratioof Br/H in the brominated compound or compounds is ≧0.5.
 4. Pyrotechniccharge according to one of claims 1 or 2, wherein the molar ratio ofBr/M^(n+) in the brominated compound or compounds is ≧n, where M is analkali or alkaline-earth metal.
 5. Pyrotechnic charge according to claim1 or 2, wherein one or more compounds from the group comprisingbrominated hydrocarbons with a melting point of >100° C., brominatedaromatic compounds, brominated aromatic carbonyl compounds, brominatedaromatic carboxylic acids and lactones are included as a fuel. 6.Pyrotechnic charge according to claim 1 or 2, wherein one or morecompounds from the group of alkali and alkaline-earth metal bromates andperbromates are included as oxidants.
 7. Pyrotechnic charge according toclaim 1 or 2, wherein one or more compounds from the group of alkali andalkaline-earth metal nitrates, dinitramides and peroxides are includedas oxidants.
 8. Pyrotechnic charge according claim 1 or 2, wherein thefuel is included in a proportion by mass of approximately 10% toapproximately 55%.
 9. Pyrotechnic charge according to claim 1 or 2,wherein the oxidant is included in a proportion by mass of approximately40% to approximately 85%.
 10. Pyrotechnic charge according to claim 2,wherein the binder is included in a proportion by mass of 0% toapproximately 5%.